class Steep::Subtyping::Relation

def ==(other)
  other.is_a?(self.class) && other.sub_type == sub_type && other.super_type == super_type
end

def flip
  self.class.new(
    sub_type: super_type,
    super_type: sub_type
  )
end

def hash
  self.class.hash ^ sub_type.hash ^ super_type.hash
end

def initialize(sub_type:, super_type:)
  @sub_type = sub_type
  @super_type = super_type
end

def map
  self.class.new(
    sub_type: yield(sub_type),
    super_type: yield(super_type)
  )
end

def to_s
  "#{sub_type} <: #{super_type}"
end